The present invention relates to a gain control mechanism, and more particularly, to an automatic gain control method and apparatus for a receiver.
For Digital Video Broadcasting (DVB) receivers supporting terrestrial (DVB-T) or handheld (DVB-H) transmissions, more and more receivers are adopting silicon tuners instead of “can” tuners in order to reduce power consumption and circuit layout area. What's more, many silicon tuners are adopting direct conversion receiver (DCR) architecture for reducing the number of components and production cost.
Please refer to FIG. 1. FIG. 1 is a simplified block diagram illustrating a silicon tuner with DCR architecture 100. As shown in FIG. 1, the typical silicon tuner with DCR architecture 100 includes a radio frequency voltage gain amplifier (RF-VGA) 110, a voltage-controlled oscillator (VCO) 120, an in-phase mixer 130, a quadrature mixer 132, an in-phase low-pass filter (LPF) 140, a quadrature low-pass filter 142, an in-phase baseband voltage gain amplifier (BB-VGA) 150, a quadrature baseband voltage gain amplifier 152 and a wide band power detector (WBPD) 160 implemented therein. The radio frequency voltage gain amplifier 110 is coupled to the in-phase mixer 130 and the quadrature mixer 132, where the in-phase mixer 130 is coupled to the in-phase low-pass filter 140 and the voltage-controlled oscillator 120, and the in-phase low-pass filter 140 is coupled to the in-phase baseband voltage gain amplifier 150. Similarly, the quadrature mixer 132 is coupled to the quadrature low-pass filter 142 and the voltage-controlled oscillator 120. The quadrature low-pass filter 142 is coupled to the quadrature baseband voltage gain amplifier 152. The wide band power detector 160 is coupled to the radio frequency voltage gain amplifier 110. The radio frequency voltage gain amplifier 110 is used to receive and amplify an RF input signal Sin, while the in-phase baseband voltage gain amplifier 150 and the quadrature baseband voltage gain amplifier 152 are used to receive and amplify the filtered signals generated from the in-phase low-pass filter 140 and the quadrature low-pass filter 142, respectively, and output an in-phase output signal Sout.I and an quadrature output signal Sout.Q, respectively. The wide band power detector 160 is used to detect the wide band signal strength and to output the related information I. Since the detailed operation of the other components in the typical silicon tuner 100 are well known to those skilled in the art, further description is omitted here for the sake of brevity.
In a silicon tuner with DCR architecture, the in-phase baseband voltage gain amplifier and the quadrature baseband voltage gain amplifier are controlled by an auto gain controller (AGC) (not shown in FIG. 1) implemented in a baseband circuit. As known to those skilled in the art, the control accuracy of the auto gain controller dominates the acquisition time and overall performance of the DVB receiver. An optimum operation point of the auto gain controller is affected by several factors: noise characteristics of the silicon tuner, non-linear characteristics of the silicon tuner, the strength of the desired signal, the frequency and strength of the interference signals, fading channel variance, and so on. Because these factors are inter-related, finding an optimum operation point it is not an easy task.